1. Field of the Invention
The present invention relates to a method for producing an electronic device. In more detail, the present invention relates to a method for producing an electronic device such as a semiconductor integrated circuit, a semiconductor device or a surface acoustic wave (SAW) device.
2. Description of the Related Art
Various electronic devices comprise patterned electrodes or metallizations on a substrate. For example, in the case of a surface acoustic wave device, an aluminum electrode is formed on a single crystal piezoelectric substrate by reactive ion etching (RIE). More specifically, as shown in FIGS. 1A and 1B, the surface of an electrode film 2 provided on a single crystal piezoelectric substrate 1 is covered with a photoresist 3, and the electrode film 2 is selectively etched using a chlorine-based gas such as Cl.sub.2 or BCl.sub.3 and the patterned photoresist 3 as a mask. However, the electrode film 2 is not always completely removed and is sometimes left behind on the single crystal substrate 1 owing to heterogeneous distributions of the film thickness of the electrode film 2 or reactive ion etching rate on the surface of the single crystal substrate 1 as shown in FIG. 1A. A residue eliminating process called over-etching becomes therefore inevitable in order to completely remove the electrode film 2 without leaving any residues behind. An over-etching treatment by 5 to 50% excess of the overall etching time under the same etching condition is applied in the over-etching method, as shown in FIG. 1B, thereby slightly etching into the single crystal substrate 1.
The portions where the electrode film 2 has been removed and the single crystal substrate 1 has been exposed are exposed to chlorine plasma during the over-etching time. Consequently, the single crystal substrate 1 is damaged forming damaged layers 4 as shown in FIG. 2, thereby deteriorating characteristics of the acoustic surface wave device.
It has been a common view that the cause of the substrate damage due to over-etching described above is a physical damage caused by impact of ions colliding with the substrate during the reactive ion etching. Accordingly, the substrate damage due to ion irradiation has been suppressed by the methods of: (1) reducing the ion irradiation energy; (2) improving homogeneity of the ion etching rate; and (3) detecting the etching terminal point with high precision. However, it was impossible to completely inhibit the damage of the substrate by the conventional methods, although it can be reduced.